In July 2002,
the Quecreek mine accident in Pennsylvania revealed the deficiencies of outdated
2-D mine maps. Nine workers became trapped in a flooded coal mine for 77 hours,
even though their maps indicated that they were hundreds of feet away from the
abandoned mine. In May, an autonomous robot capable of producing 3-D maps set
out to explore the Mathies Coal Mine near West Elizabeth, Penn., about 60 miles
northwest of the Quecreek mine. Dubbed Groundhog by its inventors,
the robotic vehicle entered the 1,067-meter shaft around 11:00 a.m. on May 30
to attempt the first autonomous navigation and mapping operation of a subterranean
space.

On May 30, a team of engineers led
their robotic, 3-D-mapping robot, named Groundhog, into the Mathies
Coal Mine in Pennsylvania. Robots like Groundhog could help people make planning
decisions about land in and around abandoned mines. All photots courtesy of
Sebastian Thrun.

While members of the media watched from behind barbed-wire fences on a nearby
overpass, Groundhog rolled up to the mines entrance, stopped, took a look
around by tilting its laser sensors up and down, and then disappeared into the
shaft. For several hours, the engineers were able to pick up a radio signal
that the robot transmitted to tell them it was still active; but once the robot
rounded a bend in the shaft, all communication ceased. During the next few hours,
the engineering team could only sit and wonder what Groundhog was encountering,
and if it was making the right decisions.

If it emerges at the other end it will be a new era for mapping the underground
world, said Sebastian Thrun of Carnegie Mellons Robotics Institute,
just prior to deployment. Hes part of the team led by William Red
Whittaker and Scott Thayer that developed Groundhog, in association with Workhorse
Technologies LLC. Up to today there was no good three-dimensional volumetric
mapping technology, Thrun said.

Three-dimensional maps are a vast improvement over 2-D maps  providing
information about the structural integrity of a mine in addition to positional
data. Knowing whether an underground shaft is structurally sound can help mine
owners make decisions about alternative uses of a shaft. In the case of the
Mathies mine, they are considering running a water processing pipeline through
the shaft. Structural information can also help people who own land above abandoned
mines make building decisions.

But Groundhog provides another  and perhaps more important  service:
It keeps humans out of abandoned mines. A robot can create a more complete map
by probing the recesses of the mine that may not be safe for human surveyors.
Should a shaft collapse, the loss of a robot is preferable to the loss of life.
This type of technology will enhance mine safety, says Bill Plassio
of the Pennsylvania Department of Environmental Protection, which provided a
grant to support the development of Groundhog. He estimates there are approximately
8,000 to 9,000 abandoned mines in western Pennsylvania alone, so the need for
reliable mapping technology is great.

Combining these technological and safety benefits into a working prototype involved
solving many hardware and software challenges. To overcome the problems of traversing
the rough terrain inside the limited space of a mine shaft, the researchers
designed Groundhog as a rugged four-wheel vehicle. Weighing about 1,600 pounds,
and measuring approximately 37 inches high by 39 inches wide by 60 inches long,
it is powered by six 8-volt batteries that provide about 10 hours of operation.
Electronic components sit in an explosion-proof enclosure to prevent ignition
of mine gases; gas sensors provide additional safety by enabling a shutdown
of the vehicle in the event of dangerous concentrations. A gyroscope keeps the
vehicle on course; tilt sensors prevent it from tipping over; and float sensors
tell Groundhog when it has wandered into water too deep for it to handle. On
both the front and rear of the vehicle, sensor units containing a 180-degree
laser range finder, headlights and a low-light camera make it possible for Groundhog
to back up if it encounters an obstacle. The sensor units swivel up and down
to look at the ceiling and the floor of the mine shaft, checking for obstacles
or roof subsidence that might prevent its passage, while constantly scanning
the walls at the same time. The echo of the laser light provides
the data needed to determine the distance to a particular object.

Although Groundhog
has explored other mines over the past year, the first real test of this mission
was the robots autonomous operation in Mathies mine. Once the start
command was given, Groundhog was on its own. The engineers could not issue instructions;
sophisticated software onboard the robot was responsible for all movement decisions.
Using its laser sensors, Groundhog attempted to map out a safe path to travel,
avoiding holes, water and other obstacles in its path. The fundamental
logic is like a rat in a maze, Whittaker said. Groundhog is discovering
its environment and making decisions as it goes along. All the while,
it stored 3-D data on the shape of the shaft in its onboard memory.

The Carnegie Mellon team monitors Groundhogs
movements and decisions as it traverses the abandoned mine. After traveling
308 meters, the robot decided to turn back after encountering a fallen roof
beam in the middle of the shaft.

At 1:44 p.m., Thrun announced that Groundhog had traveled 308 meters into the
mine, where it encountered an insurmountable obstacle. At this point it
made the absolutely perfect decision  I cant move forward, so Ill
go back, Thrun said. After traveling about 130 meters in reverse, the
robot began to malfunction. The engineers were able to download some data from
Groundhogs memory at this point: The data showed that it had encountered
a fallen roof beam in the middle of the shaft at the 308-meter point.

Shortly after the downloading operation, operators lost radio communication
with Groundhog. At about 2:50 p.m., they called the mission off, with the robot
still in the mine. Later, mine safety officials obtained the necessary clearances
to enter the mine and manually restart the robot, which enabled the team to
retrieve Groundhog and download its data.

Despite the aborted run, the team was satisfied with Groundhogs performance.
We achieved autonomous navigation without communication with the robot,
Thrun said. They were also able to provide the mine owner with valuable information
on the structural integrity of the shaft.

Im hopeful that we can develop this technology into a useful tool,
Plassio says, but we have a long way to go.

Said Whittaker: Today was just planting a first seed. We now have
a new toolkit in the mining, mapping and rescue trade. Future developments
might include cigar-shaped robots that can be dropped into bore holes and then
unfold into roving vehicles once inside the shaft. Researchers are also looking
into robotic minefish capable of maneuvering through and mapping
flooded shafts. Along with Groundhog, such robots could give miners the information
they need to prevent another Quecreek incident.